Platform buoyant understructure

ABSTRACT

The invention relates to a floatable understructure for a marine platform or deck located in an offshore body of water. The understructure includes an elongated rigid column unit incorporating buoyancy means so disposed to permit the attitude of the structure to be controlled. In the operating position, one end of the understructure is operably connected to an anchor resting on the ocean floor. The structure other end is buoyed up such that the unit assumes a generally upright disposition in the body of water with a portion protruding beyond the water&#39;&#39;s surface to support the working deck or platform.

United States Patent [191 Mott i5 1 PLATFORM BUOYANT UNDERSTRUCTURE [75]Inventor: George E. Mott, Metairie, La.

[73] Assignee: Texaco Inc., New York, NY. I [22]- Filed: April 30, 1970i [21] Appl. No.: 33,407

v 52 US. Cl... Q....61/46.s 51 Int. Cl ..B63b 21/50, E02b 17/00 58 FieldofSearch ..6l/46.5,69,81

[56] References Cited UNITED STATES PATENTS 451 Feb. 6, 1973 4/1963Popper ..6l/46.5 6/1966 Clark ..6l/46.5X

Primary Examiner-Jacob Shapiro Attorney-Thomas H. Whaley and Carl G.Reis [57] ABSTRACT The inyention relates to a floatable understructurefor a marine platform or deck located in an offshore body of water. Theunderstructure includes an elongated rigid column unit incorporatingbuoyancy means so disposed to permit the attitude of the structure to becontrolled. in, the operating position, one end of the understructure isoperably connected to an anchor resting on the ocean floor. Thestructure other end is buoyed up such that the unit assumes a generallyupright disposition in the body of water with a portion protrudingbeyond the waters surface to support the working deck or platform 1Claim, 5 Drawing Figures PATENTEUFEB s 1915 3,714,788 SHEET 10F zPLATFORM BUOYANT UNDERSTRUCTURE BACKGROUND OF THE INVENTION well asdesirable to provide a non-rigid platform which is more amenable tomeeting excessive displacing forces such as turbulent water and highwinds. A problem encountered by the use of such non-rigid platforms isthe provision of adequate means for anchoring the unit at a desiredlocation while still permitting a safe, continuous drilling operation.

Since such platforms are readily submerged in a partially buoyantcondition, or raised to the surface whereby to be transported, theanchoring mediu should likewise be flexible in character.

Because of the enormity of a deep water floatable type drillingstructure, it is often difficult to control its attitude as it islowered to a drilling site. On the other hand the anchoring means 'orfoundation member, by virtue of its compactness of weight can readily beaccurately lowered to the ocean floor.

Toward facilitating the use of a floating, yet anchored drillingplatform, the above mentioned problems are at least partially overcomeby providing a platform understructure that is not only buoyant but isconnected at the lower end to a heavy anchoring foundation. Thus, as thelatter is controllably lowered to a drilling site it will simultaneouslyguide the buoyant platform support structure to the ocean floor.

DESCRIPTION OF THE DRAWINGS of the type contemplated anchored above anoffshore drilling site.

FIG. 2 illustrates the platform of FIG. 1 shown floating at the waterssurface.

FIG. 3 is similar to FIG. 1 showing the platform during the course ofbeing lowered to the ocean floor.

FIG. 4 is an enlarged view in cross-section taken along line 44 in FIG.1.

FIG. 5 is an enlarged segmentary view incross-section of the lower endofa support leg.

Briefly stated, the understructure includes a rigid column unit ofsufficient length to extend between the ocean floor and the waterssurface at an offshore well drilling site. Each column making up theunit is buoyantly adjustable to controllably regulate the disposition ofthe structure between the extremes of substantially vertical andhorizontal attitudes.

For positioning the understructure, the latter is provided at the lowerend with a ballastable anchor whereby to regulate the weightdistribution of the structure and the buoying capacity of the anchor.

When fully ballasted, the anchor sinks to the ocean floor, therebydrawing the structure lower end downward. By simultaneously increasingthe buoyant capacity of the column unit upper end, an upright floatingcondition is achieved.

The ballastable anchor is operably connected to the column unit lowerend by means of a flexible connector. The latter is'adjustable wherebyto alter the physical relationship of the anchor at the column lowerendin accordaneewith the unit's position during anchoring.

or moving operations.

The accompanying description is directed to an offshore platform adaptedto drill subterranean wells and includes the necessary well drillingequipment. It is appreciated however, that the basic platform and anchorarrangement could be used for offshore storage, producing or refining ofpetroleum products. As shown in FIG. 1, in the upright operatingposition the platform is aligned to drill a submerged well from thewaters surface. Drilling platform 10 comprises a working deck I 11 whichsupports. a derrick 12, draw-works 13 and other equipment ancillary to awell drilling and/or producing operation. Deck 11 is preferablysupported 50 or 60 feet beyond the surface of the water to protectequipment from high waves and exposure to the water.

The deck support or understructure 14 includes a plurality of elongatedcolumn-like-members 16, 17 and 18 which are mutually interconnected bylateral bracing members 15. The lower end of platform 10 is maintainedat a desired drilling site by an anchor 19, operably carried at thecolumn unit lower end, whereby to permit a degree of adjustingflexibility therebetween.

Referring to FIG. 2, the entire understructure 14 is shown floating atthe waters surface prior to being submerged and uprighted into thedrilling position. While at the surface, the elongated deck support unit14 assumes a generally horizontal disposition with anchor 19 connectedto, although spaced sufficiently from the column unit lower end, topermit the anchor to be floated independently thereof.

The structure and character of understructure 14 are such that thebuoyancy of the unit can be varied. Thus, its floating disposition bothin and on the water, is readily controllable. Also as will behereinafter noted, the unit is sufficiently versatile to beinterchangeably used at varying water depths by the addition to orremoval of sections at the unit lower end.

Column unit 14 comprises in essence a plurality of vertically arrangedbuoyant members 16, 17 and 18 having the major portion thereof submergedsuffiof an isosceles triangle. It is understood however that theparticular column arrangement utilized will vary with the character ofequipment carried on working deck 11, with the depth of the water, andon other design factors.

Each column, 16 for example, comprises an upper end which incorporatesone or more buoyancy tanks 21. Said tanks 21 can be incorporateddirectly into the column structure or may be positioned externally ofthe columnmain section. The buoyant tanks comprise a plurality ofindividual smaller tanks spaced about the column periphery, rather thana single unit. In the present arrangement, buoyant tanks 21 are formedwith a diameter substantially greater than the diameter of the columnmain section whereby to control the column uplift force. Tanks 21 asshown, are disposed completely around the leg member 16, encased withinan outer sheath or cover.

- removed, and subsequently re-installed on the structure when thelatter is at a new drilling site.

The lower end of column unit 14 includes an elongated main section 23depending downwardly from the ,lower side of tank portion 21. Said lowermain section 23 comprises preferably a composite member formed 1 ofindividual lengths of end-welded cylindrical tubing. Said lower sectionneed not be water tight for its entire length, but is rather providedwith longitudinally arranged controlled buoyancy tanks to permit theunit to be more closely regulated during transition periods ofsubmerging and raising. Thus, as the understructure is I utilized invarious water depths, the discrete sections of cylindrical tubing can beeither added to, or removed from the column lower end whereby to adjustthe length of the leg as needed.

Said main or lower section 23 can be further provided with internalmeans such as liquid storage tanks, piping manifolds, and similaraccessories peculiar to an offshore operation.

The respective columns 16, 17 and 18 are maintained in a spaced aparthorizontal relationship by intermediate leg spacers 26 and 27 whichfunction to rigidize and brace the legs or'columns.

As shown in FIG. 1, anchor 19 depending from the lower end of columnunit 14 comprises a holding or stabilizing member of sufficient bulkthat, when positioned at the floor of a body of water, will resistdisplacing movement of the column unit. Thus, said anchoring member 19includes a relatively heavy, broad base 28 having one or more upstandingconnector posts 29 and 31 depending upwardly therefrom. The latter areadapted to operably engage a corresponding elongated socket formed inthe leg lower end. Thus, when in the fully submerged. position,understructure l4, and anchor 19are disposed in sliding engagement toallow the structure a degree of both pivotal and vertical movement whilebeing maintained in a stable drilling position.

One embodiment of a connector for operably engaging anchor 19 with theunderwater structure 14, is

shown in FIG. 5 wherein leg 16 slidably engages a corresponding anchorconnector post 29. In the instance ofleg 16, the lower end thereof isprovided with a bearing ring'36, which is integral with the connector atleg 16 lower end. Said ring 36 functions to slidably engage connectorpost 29 when the understructure 14 is uprightly positioned at a drillsite. The ring further serves to guide cable 44 when said understructureis being lowered from a horizontal floating position. 7

Body 37 of ring 36 is generally cylindrical in shape, having aninletaperture 39 at the end opposite to a flange 38 which fastens to thelower face of leg 16. The inlet aperture 39 is relatively wide,terminating in a peripheral lip 41. The latter in turn blends into asmoothly contoured side wall which forms a longitudinal guide passage 42through said body 37.

thereof and permit vertical and pivotal movement of column unit 14 whenthe legs of the latter are properly received on the respective anchorcolumns.

The upper end of each connector post 29 and 31 receives the lower end ofa flexible element such as a cable 44, chain or the like. In the instantarrangement cable 44 is shown connected to the upper end of connectorpost 29, and thereafter being registered through the constricted guidepassage 42 of bearing ring 36. Connector cable 44 functions to vary thespatial relationship between the respective anchor posts andcorresponding bearing rings in legs 16 and 17. Thus, the upper end ofcable 44 is engaged to a wind-up mechanism'including a reel or powerdriven winch 46.

Wind-up mechanism 46 is located at column 14 upper end or on deck 1].

ln practicing the method for manipulating the disclosed marine platform,the entire unit, including anchor 14, is normally fabricated at a shorelocation and thereafter towed to a point of usage at an offshore welldrilling or producing site. Thus, and as shown in FIG. 2, column unit 14is floatably supported at the waters surface on at least two of theelongated columns, i.e., 17 and 18. Such a disposition is maintained byadjusting the buoyancy of the respective buoyancy tanks 21, as well asthe supplementary buoyancy tanks within the respective columns, wherebyto minimize strain along the length of the column unit as it floats atthe water's surface.

Anchor 192s shown can be provided with self-supporting means includingpermanent or detachable buoyancy means. However, the anchor can also besup-' portably held by the floating understructure 14. Cable 44 isunreeled sufficiently to permit anchor 19 to be submerged from the lowerend of the structure 14, or to be floated independently thereof.

At a drilling site where it is determined that the platform is to besubmerged, the buoyancy system in both the anchor 19 and understructure14 are adjusted whereby to cause the anchor as well as the lower end ofsaid column unit to sink through the water. The column unit upper end ismaintained at the waters surface by adjusting the buoyancy of tanks 21.

After the anchor 19 arrives at the ocean floor, anchor posts 29 and 31are drawn into the respective leg bearing rings 36 by retracting cable44 as to slidably register the anchor post 29 within the guide passage42.

Thereafter anchor 19 is ballasted, or otherwise permitted to become atleast partially imbedded in the soft substratum. The position of seatingring 36 on the anchoring post 29 is adjusted by varying the buoyancy oftanks 21 at the structure upper end whereby the slidable relationship ismaintained between the legs and the anchor as the column unit tends tooscillate and move vertically in response to wave movement at the waterssurface. 2

Because of the relatively elongated structure of the column unit therewill be a minimum of vertical movement in response to the ordinary wavemovement at the waters surface. Even in the instance of turbulent waterandrelatively high waves, the vertical movement of the elongatedstructure will still be minimized and dampened. In effect, thedisposition of the drilling'equipment maintained on deck 11 will bestabilized re! gardless of the condition of the wind and waves in thevicinity of the marine platform.

If it becomes necessary to move platform to another site, anchor 19 israised by deballasting and dislodging it from the substratum.Simultaneously, the buoyancy of tanks 21 is adjusted so that anadditional uplift force is applied to the anchor. By adjusting thebuoyancy of the tanks 21 at the column upper end, the latter will imposea gradual uplifting force to the anchor until the latter is dislodgedfrom its normal resting place. As the entire unit becomes free of itsanchoring spot, cables 44 can be payed out and adjusted to a desiredlength. The entire unit can now be towed to the next drilling spot in asubstantially vertical disposition with the anchor disengaged from thefloor. Alternately, for long tows, understructure 14 as wellas anchor 19can be raised to the waters surface as shown in FIG. 2. Thereafter atthe new drilling site the procedure for lowering the anchor andadjusting the column unit into vertical disposition is repeated.

Obviously, many modifications and variations of the invention, ashereinbefore set forth, may be made without departing from the spiritand scope thereof, and therefore only such limitations should be imposedas are indicated in the appended claims.

I claim:

1. In a marine platform for use in an offshore body of water, comprisinga plurality of elongated, controlled buoyancy legs having engaging endsthereof, said platform being adapted to position said buoyant legs inhorizontal or vertical disposition within said body of water, and anchormeans removably connected tothe engaging ends of said respective legswhereby to be supported in the water by said buoyant legs, or toposition said platform when said anchor is lowered to a fixed locationat the ocean floor with said legs in a substantially verticaldisposition, said anchor means including a plurality of upstandinganchor posts positioned in alignment with said elongated legs when thelatter are disposed in said vertical disposition, and cable meansextending longitudinally of said legs and being connected to an anchorpost whereby to operably connect said legs and said anchor means, theimprovement therein of;

a bearing ring including a body having a flange at one end thereofconnected to said leg, guide passage means extending longitudinally ofsaid body and terminating-at an enlarged inlet aperture at said body endopposite to said flange, said guide passage means being progressivelynarrowed from said enlarged inlet aperture to a constricted portion ofsufficient opening, to slidably resister about said anchor post wherebyto permit restricted vertical oscillatory movement of said platform,said guide passage means intermediate said inlet aperture and saidconstricted portion, being further defined by a gradually curvedconfiguration to permit smooth passage of said cable through saidpassage means during movement of said anchor with respect to said legswhen the latter is separated from said anchor posts.

1. In a marine platform for use in an offshore body of water, comprisinga pluraliTy of elongated, controlled buoyancy legs having engaging endsthereof, said platform being adapted to position said buoyant legs inhorizontal or vertical disposition within said body of water, and anchormeans removably connected to the engaging ends of said respective legswhereby to be supported in the water by said buoyant legs, or toposition said platform when said anchor is lowered to a fixed locationat the ocean floor with said legs in a substantially verticaldisposition, said anchor means including a plurality of upstandinganchor posts positioned in alignment with said elongated legs when thelatter are disposed in said vertical disposition, and cable meansextending longitudinally of said legs and being connected to an anchorpost whereby to operably connect said legs and said anchor means, theimprovement therein of; a bearing ring including a body having a flangeat one end thereof connected to said leg, guide passage means extendinglongitudinally of said body and terminating at an enlarged inletaperture at said body end opposite to said flange, said guide passagemeans being progressively narrowed from said enlarged inlet aperture toa constricted portion of sufficient opening, to slidably resister aboutsaid anchor post whereby to permit restricted vertical oscillatorymovement of said platform, said guide passage means intermediate saidinlet aperture and said constricted portion, being further defined by agradually curved configuration to permit smooth passage of said cablethrough said passage means during movement of said anchor with respectto said legs when the latter is separated from said anchor posts.